1. Field of the Invention
The present invention relates to a balloon catheter used for intra aortic balloon pumping which is a method of emergency treatment for patients suffering from low heart output due to acute cardiac insufficiency etc.
2. Description of the Related Art
Intra aortic balloon pumping (hereinafter abbreviated as "IABP") is a method of assisted circulation for treatment at times of reduced heart action, such as cardiac insufficiency, wherein a balloon catheter 2 comprised of a synthetic polymer material is inserted into the aorta as shown in FIG. 7 and the balloon portion 4 is expanded and contracted in accordance with the heart beat by introducing into and leading out from the balloon portion 4 a pressurized fluid from a catheter tube 6 by a pumping system 8 so as to assist the heart action.
As the balloon catheters usable for the IABP method, there are known the balloon catheters shown in Japanese Unexamined Published Patent Application (Kokai) No. 63-206255 and Japanese Unexamined Published Patent Application (Kokai) No. 62-114565. In such balloon catheters, for the balloon portions to expand and contract in accordance with the beat of the heart, it is necessary to detect the heart beat of a patient. As a means for detecting the heart beat of the patient, there is the means of attaching electrodes to the surface of the patient's body or in or outside of the heart and detecting the heart beat as an electrical signal.
As a means for judging if the method of assisted circulation of the IABP method is suitable or not from the blood pressure of the patient, there is the method of using a balloon catheter as shown in FIG. 8(a). In this method, an opening 5 is provided at the tip of the balloon portion 4 of the balloon catheter 2. An inner tube 10 communicating with this opening 5 is inserted inside the balloon portion 4 and the catheter tube 6 in the axial direction. By measuring the fluctuation in the blood pressure near the tip from the opening 5, it is possible to observe the effects of the method of assisted circulation of the IABP method.
However, there are the following problems in such a balloon catheter 2. As shown in FIG. 8(b), the catheter tube 6 of the balloon catheter 2 is inserted into the blood vessel by being snaked along the arterial blood vessels of the patient. Therefore, the inner tube 10 for measurement of the blood pressure ends up disposed irregularly snaked inside the catheter tube 6. As a result, when the pressurized fluid for expanding or contracting the balloon portion 4 flows through the gap between the outer wall of the inner tube 10 and the inner wall of the catheter tube 6, turbulence is caused, which increases the energy loss of the fluid and reduces the efficiency of the pump system 8 shown in FIG. 7 and also can cause deviation in the timing of the expansion and contraction. The period of the expansion and contraction of the balloon portion is a short period of about 0.6 second. The fluid reciprocates inside the catheter tube 6 during that short period, so the smaller the channel resistance the better.
Further, the conventional balloon catheters usable for the IABP method conform to the physical constitutions of specific people, they do not necessarily conform to the physical constitutions of other people and therefore, it has been pointed out, there is a danger of a detrimental effect on the blood flow in the celiac artery and the renal artery. To eliminate this problem, as disclosed in Japanese Unexamined Published Patent Application (Kokai) No. 63-206255, a balloon catheter has been developed which has dimensions and a shape conforming to the physical constitution of all people as well. Further, attempts are being made to adjust the maximum diameter and length of the balloon portion in accordance with the shape of the blood vessels of the individual patients subjected to the IABP method.
Such attempts are so as to prevent the side effect of damage to the patient's blood vessels due to the diameter of the balloon portion at the time of expansion becoming larger than the inner diameter of the patient's blood vessels, which infrequently occurs, and to prevent the side effect of embolism caused by damage to the balloon portion and leakage of drive gas from the balloon portion due to the outer circumference of the balloon portion sliding in contact against calcified deposits in the patient's blood vessels. It is desirable to adjust the maximum diameter and length of the balloon portion in accordance with the state of the patient's blood vessels, but the patient's blood vessels vary greatly in shape and making the volume of the balloon portion unnecessarily small to design to the safe side is not desirable considering the principle of the IABP method.
Further, measurement of the precise dimensions of a patient's blood vessels is fully possible technically, but when considering the burden on the patient and the trouble to the doctor, this is not necessarily a realistic means of solution.
The balloon portions of all IABP method balloon catheters currently on the market, including the balloon catheter disclosed in the above publication, are shaped with fixed sectional areas along the longitudinal direction or are shaped with the tip side and the end side substantially symmetric.
The present inventors have discovered a shape of a balloon catheter wherein it is possible to effectively prevent the side effect of damaging the patient's blood vessels by fundamentally changing the shape of the conventional balloon catheter and the side effect of embolism caused by damage to the balloon portion and leakage of the drive gas from the balloon portion due to the outer circumference of the balloon portion sliding in contact with calcified deposits in the patient's blood vessels and thus have completed the present invention.